3. Herceptin

Roche expects Herceptin competition in the second half of 2019. Biosims are already eroding sales in Europe. (Roche)

Company: Roche 

2018 U.S. sales: $2.908 billion
Disease: HER2-positive breast cancer, HER2-positive metastatic gastric or gastroesophageal junction adenocarcinoma
Competition expected: Second half of 2019

Herceptin is another Roche blockbuster bracing for biosimilars this year, underscoring the massive threat the Swiss cancer giant faces from the budding class of copycats. Roche hasn't predicted just how much Herceptin will suffer from the new entrants, but it's obvious the competition will be fierce. Three Herceptin biosimilars have already won FDA approval, and that could put some serious pressure on the entrenched brand. 

Approved in 1998, Herceptin has become a staple for treating HER2-positive breast cancer, and last year, the drug pulled in $2.9 billion in the U.S., Roche reported. The drug loses a key patent on June 18, and the company has said it's expecting biosimilars to debut in the second half.

Celltrion, Samsung and Mylan each boast U.S. biosimilar nods. Since it was first rolled out for sale, the drug has pulled in $36.5 billion in the U.S., according to Evaluate.

As Roche readies for U.S. competition to Herceptin, the company hopes it can rev up its successor drug Kadcyla, which also treats HER2-positive breast cancer. That combo drug—which pairs Herceptin with a chemotherapy called DM1—won FDA approval in 2013 but has yet to perform up to Roche's expectations.

The so-called armed antibody initially carried peak sales projections of up to $5 billion—and Roche had high hopes it would take the sting out of Herceptin copycats—but last year's sales rang in at just $979 million. Still, Roche has its eye on expanding Kadcyla into new patient groups, as evidenced by its recently published data in early breast cancer. 

RELATED: Roche aims for Kadcyla expansion with new early breast cancer data 

Along with Rituxan and Herceptin, Roche also expects cancer blockbuster Avastin to face U.S. biosim competition in the second half of 2019. Together, the drugs pulled in more than $10 billion in the U.S. last year. The competition doesn't come as a surprise, of course; Roche executives have long expected biosimilars to take a bite out of the brands. The only uncertainty along the way has been timing.

New U.S. competition will trail European biosim entry for Rituxan and Herceptin, and the Roche cancer drugs are already losing ground to copycats. In 2018, Rituxan sales slipped 47% in Europe, while Herceptin fell 16%, Roche reported. 

3. Herceptin